Conventionally, chlorofluorocarbons, which are fluids that hold and efficiently carry thermal energy, has been used as refrigerants used in refrigeration cycles. However, following the adoption of the Montreal Protocol in 1987, the use of these chlorofluorocarbons has begun to be curtailed, and artificially developed substitute chlorofluorocarbons, whose ozone depletion potential is low, are coming to be used as refrigerants.
For example, in Japanese Patent Publication No. 2004-218972, there is proposed, as a method that employs a substitute chlorofluorocarbon to update conventional air conditioning equipment, a method of removing iron chloride that is mixed into a refrigerant as an impurity. Here, there is proposed a method where a conventional CFC refrigerant or HCFC refrigerant is recovered by vacuuming, a relatively eco-friendly HFC refrigerant is introduced to a refrigeration cycle, the HFC refrigerant is recovered and passed through activated carbon in order to adsorb and remove the iron chloride, and thereafter the HFC refrigerant is reintroduced to the refrigeration cycle.
However, following the further adoption of the Kyoto Protocol in 1997, the use of these substitute chlorofluorocarbons also, whose global warming potential is relatively high, is being limited; in 2001, the Chlorofluorocarbon Recovery and Destruction Law, which requires that chlorofluorocarbons be properly recovered when devices are disposed of, was issued, and the development of new substitute refrigerants and technologies that utilize those new substitute refrigerants are attracting attention.
Additionally, as these substitute refrigerants, there are natural refrigerants such as carbon dioxide, ammonia, hydrocarbons (isobutene, propane, etc.), water, and air. These natural refrigerants are materials that have the property that, when compared with the aforementioned chlorofluorocarbons and substitute chlorofluorocarbons, their GWP (Global Warming Potential) value is extremely low.
Among these, carbon dioxide is known as a material whose ozone depletion potential is zero, whose global warming potential is also much lower in comparison to conventional refrigerants, which has no toxicity, is nonflammable, and whose efficiency in creating a high temperature is good among natural refrigerants, and from environmental/energy aspects and safety aspects, carbon dioxide is garnering attention as a refrigerant in air conditioners.